Low quality when adding titles (Videostudio 2018)

Hi guys! (First of all, sorry for my english, is not my mother language and maybe I'll make some mistakes...)
I'm making my holiday video and I usually add some title showing the name of the place. The problem is when I export the project to a file, when the titles appears in screen the quality gets lower while the title is showing, showing some saw-teeth and blur, when the title dissappears automatically the quality increase to the original one. The original files are Interlaced, upper field first. I usually export with the option "same as first video clip" but I tried so many options, doubling the bitrate, changing fields order, mpeg optimizer, two pass encode... and the same happens.
The only way this doesn't happen is if I export changing upper lower first to frame based. The point is that if I do that, maybe there is a little loss of quality, right?
What can I do for not lose quality? I need necessary convert it to progressive with frame based option? Will I lose quality of the whole video with it?
I uploaded the snapshots to show you what I mean https://ibb.co/mbbseT

I'm making my holiday video and I usually add some title showing the name of the place. The problem is when I export the project to a file, when the titles appears in screen the quality gets lower while the title is showing, showing some saw-teeth and blur, when the title dissappears automatically the quality increase to the original one. The original files are Interlaced, upper field first. I usually export with the option "same as first video clip" but I tried so many options, doubling the bitrate, changing fields order, mpeg optimizer, two pass encode... and the same happens.
The only way this doesn't happen is if I export changing upper lower first to frame based. The point is that if I do that, maybe there is a little loss of quality, right?
What can I do for not lose quality? I need necessary convert it to progressive with frame based option? Will I lose quality of the whole video with it?
I uploaded the snapshots to show you what I mean https://ibb.co/mbbseT
