TYPO3 Core

I can confirm this issue using the following setup:

temp.mainMenu.10 = HMENU
temp.mainMenu.10 {
  entryLevel = 0
  1 = GMENU
  1.expAll = 1
  1.wrap = <ul class="firstLevel">|</ul>
  1.NO = 1
  1.NO {
    allWrap = <li>|</li>
    XY = [10.w]+10,[10.h]+10
    backColor = #ffffff
    transparentColor = #ffffff
    transparentBackground = 1
    10 = TEXT
    10 {
      text.field = title
      text.noTrimWrap = | -- | |
      fontSize = 14px
      fontFile = fileadmin/fonts/momstypewriter.ttf
      fontColor = #535f5f
      offset = 0,26
    }
  }
  1.ACT < .1.NO
  1.ACT {
    allWrap = <li class="current">|</li>
  }
}

The issue is caused by the implementation of the optionSplit. Specifically by an explode pattern '||' used in t3lib_TStemplate::splitConfArray. This pattern can also occur in a noTrimWrap wit different semantics.

Patch set 1 for branch master has been pushed to the review server.
It is available at http://review.typo3.org/9428

Applied in changeset 8feaf17bc84d008dc41a1f1de0e0cb4248ba2cdb.