pattern-spam on pattern-edit if clone of the pattern-filled object exists

[su_v]

Follow-up report to
Bug #674109 “Pattern spam when adjusting a pattern in text.”
<https://bugs.launchpad.net/inkscape/+bug/674109>

Based on "Bug? Moving/scaling a pattern spawns multiple new patterns"
<http://www.inkscapeforum.com/viewtopic.php?f=5&t=6295>

Steps to reproduce:
1) create a pattern-filled object
2) create a clone of the pattern-filled object
3) adjust the pattern of the original

Expected result:
the current definition of the pattern referenced by the object is updated (adding at most one more definition with the 'transform' attribute).

Actual result:
multiple pattern definitions are created in a chain, each containing only a transformation and a reference to the previous pattern.

4) delete or unlink the clone
5) adjust the pattern of the original

Result:
no more pattern spam (the referenced definition is updated)

Tested and reproduced with Inkscape 0.48.0 and 0.48+devel r9982 on OS X 10.5.8

[su_v (suv-lp)]

Setting to 'Confirmed' as this report is based on reproducing the problem as it was detailed in the forum topic.

[Beluga (buovjaga)]

Reproduced spamming in XML editor view.

Arch Linux 64-bit, KDE Plasma 5
Inkscape 0.92pre1 15054 (GTK3)