Reproducable on different machines (debian-based) with version 1.1.28, 1.1.19 and git master.

+ Trace 237067

Reproducable with following minimal example:

#include <string.h>
#include <libintl.h>

#include <libxslt/xslt.h>
#include <libxslt/transform.h>
#include <libxslt/xsltutils.h>
#include <libxslt/extensions.h>

#define UNUSED __attribute__((__unused__))

#define XSLT_MODUL_URI "http://test.uri"

static void XsltGettext(xsltTransformContextPtr ctxt, xmlNodePtr node, xmlNodePtr inst, UNUSED xsltStylePreCompPtr comp)
{
    xmlChar *text;

    if(ctxt == NULL||node==NULL||inst==NULL||ctxt->insert==NULL) {
        xsltGenericError(xsltGenericErrorContext, "error\n");
        return;
    }

    text = BAD_CAST gettext("text");
    node = xmlNewText(text);
    xmlAddChild(ctxt->insert, node);
}

static void* xsltInitFct(xsltTransformContextPtr ctxt, UNUSED const xmlChar *URI)
{
    xsltRegisterExtElement(ctxt, (const xmlChar*)"gettext", (const xmlChar*)XSLT_MODUL_URI, (xsltTransformFunction)XsltGettext);

    return NULL;
}

static void xsltShutdownFct(UNUSED xsltTransformContextPtr ctxt, UNUSED const xmlChar *URI, UNUSED void *data)
{}

int main(UNUSED int argc, UNUSED char **argv)
{
    xsltStylesheetPtr cur;
    const char *params[1] = {NULL};
    xmlDocPtr xslDoc = NULL, xmlDoc = NULL, htmlDoc = NULL;

    const char *xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\
<test>\
<sub><s>startdate starttime</s><e>enddate endtime</e></sub>\
</test>";
    const char *xsl = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\
<xsl:stylesheet xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\" version=\"1.0\" xmlns:test=\"http://test.uri\" extension-element-prefixes=\"test\">\
  <xsl:template match=\"test\">\
    <xsl:for-each select=\"sub\">\
      <a><xsl:value-of select=\"position()\"/>. <test:gettext>sub</test:gettext> : <xsl:value-of select=\"s\"/><test:gettext> till </test:gettext><xsl:value-of select=\"e\"/></a>\
    </xsl:for-each>\
  </xsl:template>\
</xsl:stylesheet>";

    xmlSubstituteEntitiesDefault(1);
    xmlLoadExtDtdDefaultValue = 1;

    xsltRegisterExtModule((const xmlChar*)XSLT_MODUL_URI, xsltInitFct, xsltShutdownFct);

    xmlDoc = xmlReadMemory(xml, strlen(xml), "test", NULL, XML_PARSE_NOBLANKS);
    if(xmlDoc == NULL)
        return 1;
    xslDoc = xmlReadMemory(xsl, strlen(xsl), "stylesheet", NULL, XML_PARSE_NOBLANKS);
    if(xslDoc == NULL)
        return 1;

    cur = xsltParseStylesheetDoc(xslDoc);
    htmlDoc = xsltApplyStylesheet(cur, xmlDoc, params);
    unsigned char *buf = NULL;
    int len = 0;
    xmlDocDumpFormatMemory(htmlDoc, &buf, &len, 1);
    printf("%s\n", buf);

    xsltFreeStylesheet(cur);
    xmlFreeDoc(xmlDoc);
    xmlFreeDoc(htmlDoc);
    xsltCleanupGlobals();
    xmlCleanupParser();

    xmlMemoryDump();
    return 0;
}