Looks like your monitor simply has wrong EDID values in it.  The nvidia driver is ignoring what the monitor says its capable of and firing things up at 50Hz.  It appears to believe your monitor's firmware was encoded incorrectly.

So, seems to be more of a hardware bug than nvidia or X.  From the logs look like software is compensating for the hardware problem.  Other than the unexpected refresh rate value setting are you noticing any visible issues?  If not, we can probably close this as 'not a software bug'.

[    20.799] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.799] (WW) NVIDIA(0):     mode "1280x720" is specified in the EDID; however, the
[    20.799] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.799] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.799] (WW) NVIDIA(0):     VertRefresh check for mode "1280x720".
[    20.799] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.799] (WW) NVIDIA(0):     mode "720x576" is specified in the EDID; however, the
[    20.799] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.799] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.799] (WW) NVIDIA(0):     VertRefresh check for mode "720x576".
[    20.799] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.799] (WW) NVIDIA(0):     mode "720x576" is specified in the EDID; however, the
[    20.799] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.799] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.799] (WW) NVIDIA(0):     VertRefresh check for mode "720x576".
[    20.799] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.799] (WW) NVIDIA(0):     mode "1280x720" is specified in the EDID; however, the
[    20.799] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.799] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.799] (WW) NVIDIA(0):     VertRefresh check for mode "1280x720".
[    20.799] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.799] (WW) NVIDIA(0):     mode "1920x1080" is specified in the EDID; however, the
[    20.799] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.799] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.799] (WW) NVIDIA(0):     VertRefresh check for mode "1920x1080".
[    20.799] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.799] (WW) NVIDIA(0):     mode "1280x720" is specified in the EDID; however, the
[    20.799] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.799] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.799] (WW) NVIDIA(0):     VertRefresh check for mode "1280x720".
[    20.800] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.800] (WW) NVIDIA(0):     mode "720x576" is specified in the EDID; however, the
[    20.800] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.800] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.800] (WW) NVIDIA(0):     VertRefresh check for mode "720x576".
[    20.800] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.800] (WW) NVIDIA(0):     mode "720x576" is specified in the EDID; however, the
[    20.800] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.800] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.800] (WW) NVIDIA(0):     VertRefresh check for mode "720x576".
[    20.800] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.800] (WW) NVIDIA(0):     mode "1280x720" is specified in the EDID; however, the
[    20.800] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.800] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.800] (WW) NVIDIA(0):     VertRefresh check for mode "1280x720".
[    20.800] (WW) NVIDIA(0): The EDID for Idek Iiyama PL2210HD (DFP-0) contradicts itself:
[    20.800] (WW) NVIDIA(0):     mode "1920x1080" is specified in the EDID; however, the
[    20.800] (WW) NVIDIA(0):     EDID's valid VertRefresh range (55.000-76.000 Hz) would
[    20.800] (WW) NVIDIA(0):     exclude this mode's VertRefresh (50.0 Hz); ignoring
[    20.800] (WW) NVIDIA(0):     VertRefresh check for mode "1920x1080".