So I guess it might just be an error in the older LimeSurvey Version
That is what I think.
You should really update (in my opinion the first ten releases of a new branch are still buggy - even if called "stable" )
If you have a look at the cange logs, that start here for your 2.50 version
www.limesurvey.org/about-limesurvey/update-log?start=210
you will see that nearly each day there was a new version released.
And here is something that might affect your issue.
2.50+ build 160407 & 2.50+ build 160411
-Fixed issue #10844: Various issues using the LS 2.50 default template
(but only if your question looks fine in other templates.)
If you have a lot of customized templates, it will be some work to update to 3.22 LTS, because the template structure changed from 2.50/2.73 to 3.x.
The latest release of the 2.50 branch you get here
www.limesurvey.org/lts-releases-download...24-archived-releases
limesurvey2.73.1-build171220.zip
And the latest 3.x here in the download section.
Joffm