Sentence Discussions are a user-to-user forum. If you need Technical Support, you should take a screenshot that demonstrates the issue, and submit it with a bug report. The people who can fix the sort of issue that you are describing don't read Sentence Discussions, and the people who read Sentence Discussions can't do anything to fix bugs.
Screen recorder? Just a screen-shot showing the error message. PrtScr on a Windows machine (with or without ctrl/alt/shift. Win+Alt+S for even more control) or VolDown+Power on most Android devices is all you need.
Of course if this is actually an edge-case in a "Type what you hear" exercise (why else would you be putting the answer in in Irish?) a screen recording might make that clearer, but just mentioning that condition in the problem description would be almost as good, and a lot less trouble.
Unlike many other European languages, both Irish and English differentiate between the simple present Oibríonn na fir i bportach - "The men work in a bog" and the present progressive Tá na fir ag obair i bportach - "The men are working in a bog". You can't translate a simple present sentence in Irish using the present progressive in English, or vice versa, because they do not mean the same thing.
Prepositions that lenite lenite. Prepositions that eclipse eclipse. Prepositions that don't do anything at all don't do anything. Some prepostions can lenite, or eclipse or do nothing at all, depending on circumstances.
When it comes to prepositions and indefinite nouns, there is no "usually".