Just making the card "Internal" won't make it automatically change things. Also, have you rebooted the phone since the change? That is a large factor. You may also want to check for other updates.
A simple way around this is to first, move things like photos, music, videos, etc., over to the card. They take up tons of room just like apps. You can also go into your "Settings" then tap "Apps" . From here you should be able to tap individual apps you have installed and move them over.
You should also be able to now download directly to the card from say "Google Play". It should give you the option of choosing where you want to install the app. If it isn't then something isn't working correctly. There could be something wrong with the SD card, or it could be that HTC has restricted what can be done on the device. It happens. To find out for sure, you would have to check with HTC.