Pausing SMPlayer and moving to another window hides the image

[Wiktor Nizio]

I watch video in SMPlayer, then pause and move focus to another window. The paused image in SMPlayer vanishes.

Reproducible in SMPlayer 20.x and 21.x, while multimedia engine is set to the default value "mplayer".

Not reproducible in SMPlayer 21.1.0 when the multimedia engine is set to mpv, so I believe the bug is in mplayer.

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: mplayer 2:1.4+ds1-1
ProcVersionSignature: Ubuntu 5.11.0-13.14-generic 5.11.7
Uname: Linux 5.11.0-13-generic x86_64
ApportVersion: 2.20.11-0ubuntu62
Architecture: amd64
CasperMD5json:
 {
   "result": "skip"
 }
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 8 21:13:08 2021
InstallationDate: Installed on 2021-04-08 (0 days ago)
InstallationMedia: Ubuntu 21.04 "Hirsute Hippo" - Beta amd64 (20210331.1)
SourcePackage: mplayer
UpgradeStatus: No upgrade log present (probably fresh install)