Sachin, that is some very Interesting dynamic; this is very tricky and not my expertise. Have you looked into see if there is a default theme assigned in the MIME objects in SE80? Also have you checked what solution you have implemented? Aerospace, Banking, Oil, Retail? This may not matter, but it can have some different code injected. I have done a quick search on SAP and have to recommend two related notes.
2082806 - BSP: Corrections for unified rendering (UR-mimes)
2070730 - BSP: Corrections for unified rendering (ABAP renderer)
These notes are very specific, and may not apply to your issue, I would say after checking those tw, please try these two notes also; I highly recommend 1852400 - UI theme designer (main note) / 1852401 - UI Theme Designer for SAP NetWeaver AS ABAP (main SAP Note)<-- This is more my expertise and I have good recommendation using this note as a key implementation guideline, especially for upgrades.
SAP can’t ensure that a particular theme runs in all framework or in all releases of a framework. Please check your landscape to ensure that your base theme (used in your environment directly or as start theme to create a custom theme) can be used in your frameworks!
It is technically not possible to prevent the use of a not supported theme in a framework in all cases. This must be ensured by a correct configuration.
Please update your findings as I am eagerly awaiting next steps. I have a few more suggestions.
Thank you,
-Sung