TYPO3 Core

I cannot reproduce this issue. What default configuration settings are you using? What do you have in Page TSConfig?

My default configuration setting is "typical". Changing it to demo doesn't make a difference.
And here is my page tsconfig. The exact same configuration works with older versions of the rte and typo3:
RTE.default.buttons.formatblock.removeItems = H4,H5,H6,PRE,ADDRESS
RTE.default.hidePStyleItems = H4,H5,H6,PRE,ADDRESS
#RTE.hidePStyleItems = H4,H5,H6,PRE,ADDRESS

RTE.default.contentCSS = fileadmin/templates/styles/rte.css
RTE.default.blindImageOptions = magic,dragdrop

RTE.RTEkeyList = formatblock, bold, italic, unorderedlist, link, table, chMode, removeformat, rowinsertabove, rowinsertunder, rowdelete, rowsplit, columninsertbefore, columninsertafter, columndelete, columnsplit, cellinsertbefore, cellinsertafter, celldelete, cellsplit, cellmerge
RTE.default.showButtons = formatblock, bold, italic, unorderedlist, insertcharacter, link, image, table, chMode, removeformat, rowinsertabove, rowinsertunder, rowdelete, rowsplit, columninsertbefore, columninsertafter, columndelete, columnsplit, cellinsertbefore, cellinsertafter, celldelete, cellsplit, cellmerge

RTE.default.buttons.link.popupSelector.disabled = 1
RTE.default.classesAnchor >
RTE.default {
hideTableOperationsInToolbar = 1
disableAlignmentFieldsetInTableOperations = 0
disableSpacingFieldsetInTableOperations = 0
disableColorFieldsetInTableOperations = 0
disableLayoutFieldsetInTableOperations = 0
disableBordersFieldsetInTableOperations = 0
}

RTE.classesAnchor {
externalLink >
externalLinkInNewWindow >
internalLink >
internalLinkInNewWindow >
download >
mail >
}

Ok, it seems that the tagnames need to be in lower case.

yes, that was it. many thanks!
It makes much more sense for the tagnames to be in lowercase anyway.
Still, you might want to fix it for backwards compatibility, because it used to work with uppercase tags as well...

Upper case tags honoured again with fix committed to SVN TYPO3core branch TYPO3_4-2 revision 3425.

Use t3lib_div::strtolower for Turkish backends.

Use of t3lib_div::strtolower committed to SVN TYPO3core branch TYPO3_4-2 revision 3429.