It's normal. As I understand it, Operators limit Your max character number, when encoding supporting accented characters (basically, all special ones) is used - so, You pay more, when You use special characters (because SMS is send as many small messages, merged into one upon receiving). I don't know if it is still true for all operators, but - at least - it was not so long ago.

The workaround is to check how much your operator tax You for using MMS - most of the times, 1 SMS = 1MMS (up to 100 kb), so it's sane to use *only* MMS, even for text-only messages. Also, keep in mind, that 100kb is a LOT, and You would probably got problems with writing so long message, that could hit this limit.

/Estel